Optimization of Donkey Milk Pasteurization Process

Donkey milk represents an attractive solution as new-born feeding, mainly if occur physiological limitations concerning the milk availability in post-pregnancy or bovine’s milk proteins linked to immune diseases. At present, the producers use custom-made batch pasteurization plant, with a poor temperature control system and very high time required to carry out the pasteurization process. It is due to the low availability of raw materials due to limited donkey livestock and low milk’s yield and the lack of high technology UHT pasteurization plants with limited processing capacity. In this work, an innovative low capability (30 l/h) continuous flow pasteurization plant, designed and built for High Temperature for Short Time (HTST) treatments, was characterized in the MACLab of UNIBAS. To test the plant, a matrix with three pasteurization temperatures (75, 85, 92 °C) and times (3, 7, 14 s) was tested, and the efficacy of the treatments was evaluated on microflora enumeration (L. monocytgenens, Enterobacteriaceae, total aerobic bacteria) as soon as after the treatments and over 30 days-storage at 4 °C. The HTST apparatus showed high performance; the complete eradication of Enterobacteriaceae detected the efficacy of the treatments at every time and temperatures tested. Decreasing in total bacterial count and lysozyme content was affected by treatment size. Through this methodological approach, it was possible to investigate the effect of HTST treatments (following by cooling soon) on the primary chemical and microbiological standard for donkey milk, to set up an official sanitation protocol that allows optimizing its nutritional value.